When is R² appropriate for comparing customer and supplier measurement systems?

Linear regression analysis is often used to compare paired supplier and customer measurements of a given quantitative product characteristic in a shipment of products. Specifically, the coefficient of determination, R ², is then used to determine if the supplier's and the buyer's measurement systems are in conformity, with sufficiently high values implying agreement. In this article, we show that R² istextitnever an appropriate statistic for making this determination. Examples are provided and an appropriate methodology for comparing two measurement systems is delineated.